North Diversion Channel Physical Modeling:

Transcription

1 North Diversion Channel Physical Modeling: Bike Notch Implementation Between Vineyard Arroyo Confluence to Osuna Bridge August 29, 2011 Prepared for Albuquerque Metropolitan Arroyo Flood Control Authority (AMAFCA) By UNM Hydraulics Laboratory Julie Coonrod, Ph.D., Professor Emile Kareem Saint-Lot & Tyler Gillihan, Research Assistants Department of Civil Engineering University of New Mexico 1

2 Introduction: The North Diversion Channel (NDC), built by the Corps of Engineers and maintained by Albuquerque Metropolitan Arroyo Flood Control Authority (AMAFCA), intercepts storm water from multiple open channels and carries the water north for discharge into the Rio Grande. Albuquerque utilizes the open channel storm drainage system as a transportation corridor for pedestrians and cyclists. In particular, the NDC serves as a popular north-south bike trail for Albuquerque residents (Figure 1). To accommodate cyclists, recessed bike paths (or bike notches ), have been placed in the channel at various bridge locations to allow for continuous cycling uninterrupted by motor vehicles. Figure 1: North Diversion Channel Map 2

3 The Corps requires that channel modifications not jeopardize necessary storm water conveyance at the bridges. The University of New Mexico Hydraulics Lab was utilized in 1992 to investigate such bike notches in the NDC and again in 1997 for the South Diversion Channel. The 1992 report concluded that recessed bike paths do not adversely impact flow for subcritical reaches. Furthermore, if the channel is substantially subcritical, physical modeling is not needed. The 1997 report, for a channel with a Froude number of 1.92, also showed the recess bike path did not adversely impact flow. The subjects of this study are two proposed bike notches in the NDC near Osuna Road (Figure 2). The hydraulics near both proposed bike notches are complicated by upstream tributary flows. Upstream of the proposed Singer bike notch is tributary flow from the Vineyard Arroyo. However, the tributary flow is far enough upstream that any surface wave effects of the confluence will be diminished before reaching the bike notch. Just upstream of the proposed Osuna bike notch is tributary flow from the Bear Canyon Arroyo. Osuna Bridge abutments extend into the NDC channel, further complicating hydraulics associated with this proposed bike notch. Osuna Storm Drain Actual Length: 5500 ft. Model Length: 66 ft. Model Scales: 1:84 & 1:36 Bear Canyon Arroyo Singer Osuna Bike Notch Vineyard Arroyo Singer Bike Notch Figure 2: North Diversion Channel near Osuna Road To simulate a total flow of 24,000 ft. 3 /s in the NDC, models of two scales were constructed simultaneously. First, a 1:84 scale model was used to capture both a bike notch at Osuna and Singer bridges. Second, a 1:36 scale model was used to improve effects of scale for examination of the Osuna bike notch in conjunction with Bear Canyon Arroyo confluence and Osuna Bridge 3

4 abutments. Both models were constructed primarily of ¼ inch corrugated plastic and aluminum tape. AMAFCA crews assisted in building wooden frames to support the channel. 1:84 Model: The 1:84 model includes bike notches at both Singer and Osuna bridges. Using Froude Similitude, 180 gal/min is required to simulate the NDC 24,000 ft 3 /s. A garden hose connected to a sump pump provides flow through the Bear Canyon Arroyo. This model captures both bike notches and shows the complete construction of the bike notches in the NDC. The modeled notch underneath Singer Bridge stretches 14 ft. (almost 1200 ft. in the NDC) (Figure 3). Figure 3: 1:84 Scale Singer Bike Notch The actual bridge sits above the channel and is not shown in the model. In contrast, Osuna Bridge abutments extend into the channel flow. AMAFCA provided measurements of the abutments that were used to construct the bridges. The Osuna bike notch stretches approximately 21 ft. (almost 1800 ft. in the NDC) (Figure 4). 4

5 Figure 4: 1:84 Scale Osuna Bike Notch This notch runs a greater length through the channel because of future plans for a second bridge over the NDC. Each of the two bike notches have a scaled bottom width of 1.7 in. and a scaled side length of 1.3 in (12 ft. bottom width and 9 ft. side length in the NDC). Construction of this model was completed on August 10, 2011 (Figure 5). Figure 5: 1:84 Scale Model 5

6 1:36 Model: The 1:36 scale model includes only the Osuna bike notch to allow UNM s Hydraulics Lab to quantify the results. Using Froude Similitude, 1390 gal/min would be required to simulate the NDC s 24,000 ft. 3 /s. A four inch hose connected to the main pump provides 81 gal/min, 1400 ft. 3 /s in the NDC, for the Bear Canyon Arroyo (Figure 6). Figure 6: 1:36 Bear Canyon Confluence The scaled bottom width of this bike notch is 4 in. (12 ft. on the NDC) and it has a scaled side length of 3 in. (12 ft. bottom width and 9 ft. side length in the NDC). Osuna Bridge abutments extend into the channel and can be seen in Figure 7. Any standing waves created by the Bear Canyon Arroyo confluence will be clearly visible. The black line on either side of the model marks the top of the channel. This model was completed August 10, 2011 (Figure 7). 6

7 Figure 7: 1:36 Bike Notch & Osuna Bridge Modeling: Testing of the 1:84 model showed both bike notches to have no apparent adverse hydraulic effects (Figure 8). The Bear Canyon Arroyo confluence had minor effects on the flow within the NDC and as a result no standing waves were observed. Velocity and water depth measurements are displayed in Table 1 to allow for comparison between the two scale models. Figure 8: 1:84 Bear Canyon Arroyo confluence Modeling at the 1:36 scale produced similar results to that of the 1:84 scale. The bike notch had no effect on the channel s hydraulics, additionally the results solidified conclusions of the 1:84 scale model, as there were no standing waves or adverse hydraulic effects near the Bear Canyon confluence. 7

8 Concerns: Although no issues were detected with the bike notches on the 1:84 scale model, it was discovered this model lacked detail in the area of interest where the bike notch passes underneath Osuna Bridge. This small scale inhibited, due to size, the observations of standing waves or adverse hydraulic effects; thus no further testing was necessary. During testing of the 1:36 scale model engineers from AMAFCA and City of Albuquerque (COA) noticed non-uniform flow upstream of the drop (Figure 9). This non-uniform flow would increase velocity and would diminish any effects of standing waves from the Bear Confluence. Engineers suggested introducing channel bottom roughness, to imitate sediment and test flow stability, in the NDC. Bike notch designs also include hand rails which engineers suggested could cause hydraulic effects if they became blocked. Figure 9: 1:36 Non-Uniform Flow 8

9 Addressing Concerns: A barrier was installed on the 1:36 scale bike notch to create a no flow zone and imitate a blocked hand rail (Figure 10). Figure 10: 1:36 Blocked Hand Rail To create a more uniform flow and decrease velocity makeshift cylindrical bridge piers (woodpiles) were placed into the channel. Table 2 shows data relating the velocities and water depths of four different scenarios: 1. Bike notch covered with woodpiles in the channel, 2. Bike notch covered without woodpiles, 3. Bike notch uncovered with woodpiles in the channel, and 4. Bike notch uncovered without woodpiles. Scenario one resulted in the storm water reaching the Osuna Bridge abutments (Figure 11), whereas all other scenarios showed normal flow without reaching the abutments. Figure 11: 1:36 Water reaching Osuna Bridge abutment 9

10 Table 1: Four Scenarios of 1:36 Model 1:36 Without Wood Piles 1:36 With Wood Piles Bike Notch Covered Bike Notch Covered Velocity* (ft/sec.) 5.11 Velocity* (ft/sec.) *Right before Osuna Bridge 4.56 *Right before Osuna Bridge Velocity (ft/sec.) 5.01 Velocity (ft/sec.) 4.05 Pro. Velocity (ft/sec.) Pro. Velocity (ft/sec.) Water Depth (in.) 4.4 Water Depth (in.) 5.7 Water Depth (in.) 4.7 Water Depth (in.) 6 Flow Lower (gpm) 1215 Flow Lower (gpm) 1304 Flow Upper (gpm) 1307 Flow Upper (gpm) 1379 Flow Median (gpm) 1261 Flow Median (gpm) :36 Without Wood Piles 1:36 With Wood Piles Bike Notch Uncovered Bike Notch Uncovered Velocity* (ft/sec.) 5.71 Velocity* (ft/sec.) *Right before Osuna Bridge 5.08 *Right before Osuna Bridge Velocity (ft/sec.) 5.35 Velocity (ft/sec.) 4.39 Pro. Velocity (ft/sec.) Pro. Velocity (ft/sec.) Water Depth (in.) 4.2 Water Depth (in.) 4.9 Water Depth (in.) 4.5 Water Depth (in.) 5.2 Flow Lower (gpm) 1350 Flow Lower (gpm) 1398 Flow Upper (gpm) 1499 Flow Upper (gpm) 1528 Flow Median (gpm) 1424 Flow Median (gpm) 1462 Conclusion: A 1:84 scale model and a 1:36 scale model were used to simulate 24,000 ft. 3 /s of flow through the North Diversion Channel. After running the models it was determined that the placement of the Singer and Osuna bike notches into the North Diversion Channel do not affect the channel hydraulics nor create standing waves. If the bike notch underneath the Osuna Bridge were to become blocked storm waters flowing through the NDC would reach the Osuna Bridge abutments. 10